Crystallizing process



Patented Feb. 27, 1951 UNITED STATES PATENT OFFICE CRYSTALLIZING PROCESS Application May 10, 1944, Serial No. 534,996

14 Claims.

This invention relates to a crystallizing process, and more particularly to the separation of esters of fatty acids and derivatives thereof by crystallization without the use of a foreign solvent and to the separation of fatty acids and derivatives thereof from natural mixtures into fractions of diiierent degrees of saturation by forming esters of the fatty acids or derivatives thereof and separating the esters by crystallization. If desired, the esters may be hydrolyzed to again form the fatty acids or derivatives.

The invention contemplates the separation of the esters of fatty acids from a mixture according to the degree of saturation of the various acids in the mixture. The esters of the fatty acids of the mixture are crystallized from the mixture without the use of a solvent. In the process, the fatty acids or derivatives thereof may be converted into esters in which the alcohol of the ester contains at least two carbon atoms. The esters in the form of a liquid mixture are cooled to crystallize the esters of higher melting point. If desired, by a series of successive steps of cooling, the liquid mixture may be fractionally crystallized to obtain a series of fractions of successively lower melting point. The various fractions may be separately hydrolyzed to recover the fatty acids or derivatives.

Many efforts have heretofore been made to separate fatty acids according to their melting points without the use of a solvent. It is common practice, fo example, to separate the fatty acids of lard or tallow into commercial stearic acid and red oil by a pressing operation. In this process, the mixture of fatty acids, for example, the natural mixture of fatty acids obtained from tallow and containing approximately 30% palmitic acid, 20% stearic acid, and 45% oleic acid, is subjected to successive pressing operations. The mixture at room temperature, at which the stearic and palmitic acids are solids, is pressed to remove the liquid oleic acid. The pressed solid contains palmitic and stearic acids and is known as commercial stearic acid. The liquid which is removed by the pressing contains oleic acid and is known as red oil.

Since the liquid is not effectively removed from the solid by a single pressing operation, the mixture is subjected to successive pressing operations. However, even after successive pressing operations, the separation is not efficient. In the usual commercial practice, the commercial stearic acid after the first pressing operation contains approximately 15% of oleic acid. After the second operation, approximately 10% of oleic acid remains. Then after the third pressing operation, approximately 5% of oleic acid is found to be present in the stearic acid. Thus, even triple-pressed commercial stearic acid contains a few per cent of oleic acid. Moreover, in the pressing operation, there is always some stearic acid lost by solution in the oleic acid which is removed.

The conventional pressing of a mixture of saturated and unsaturated fatty acids does avoid the use of solvent and thereby avoids the necessity of heating the separated portions to dry them and remove solvent. The pressing method also avo ds the difficulty of evaporation of solvent on the filter press which is encountered when crystals are filtered from a solvent solution. In addition, the cost and diliiculty of recovering the solvent are eliminated. Despite these advantages, the inefficiency of the separation in the pressing method is so great that efforts have long been made to improve the separation or to obtain a more efiicient type of separation.

Where fatty ac ds are separated from a mixture by a conventional pressing operation, small and poorly defined crystals are formed and a substantial quantity of occluded liquid remains in the crystals. With the present invention on the other hand, large and well defined crystals are obtained and occluded liquid in the separated crystals is minimized. The esters in which the alcohol group contains two or more carbon atoms may be much more readily and efficiently separated from each othe than are the fatty acids themselves or the methyl esters of the fatty acids. With the process of the invention, a better stearic acid product, for example, is obtained in one or two steps of crystallization than with a triple press ng operation, as used in the prior art.

The invention is illustrated in the drawing which shows a flow diagram of the steps of the crystallizing process.

The invention is applicable to any mixture of fatty acids or derivatives thereof, but is particularly suitable for separating fatty acids from a natural mixture thereof which is derived from fats or oils. For example, the invention may be effectively applied to a fatty acid mixture obtained from lard, tallow, soy bean oil, cottonseed oil, cocoanut oil, palm kernel oil, palm oil, linseed oil, castor oil, tung oil, or the like. The term fatty acids as used herein is intended to include aliphatic acids having at least six carbon atoms in the carbon chain.

The fatt acids are converted into esters in which the alcohol group contains from two to four carbon atoms. Aliphatic alcohols are used in forming the esters. For example ethyl, npropyl, or n-butyl alcohol may be used to form the esters. Ethyl alcohol is particularly desirable since it is very readily available commercially and is not poisonous. Instead of an alcohol, any compound containing the alkyl group and capable of forming an ester with the fatty acid may be used. Esterification may be carried out in any suitable or conventional manner.

In the crystallizing process, a liquid mixture of the esters of the fatty acids, in which each ester has an alcohol group containing at least two carbon atoms, is cooled until the esters of higher melting point are crystallized. The mixture is then filtered or subjected to centrifugation or the like to separate the crystals. If desired, the filtrate may be further cooled to form crystals of esters of fatty acids of the next highest melting point. In this manner, a series of steps may be carried out to perform a fractional crystallization operation.

Preferably, the crystallizing process is applied to a mixture of esters in which the alcohol group is the same. For example, the process may be applied to a mixture of ethyl esters of the fatty acids. Similarly, the process may be applied to a mixture of propyl esters of the fatty acids.

The crystallizing process is carried out without the use of a solvent and the mixture of the esters of the fatty acids is cooled from a temperature at which the entire mixture is in the liquid phase. Since the various esters of fatty acids exert some solvent action on each other and since each of the esters is therefore at least partially dissolved in the other liquid esters, the absence of solvent is indicated herein by describing the mixture as one which is substantially free of foreign solvents.

When the mixture of liquid esters of fatty acids is cooled to form a crystalline precipitate of the esters of higher melting p oint and the crystalline precipitate separated from the solution, further purification of the precipitate and the filtrate may be found desirable. If desired, the filtrate may be further cooled and successive crystalline precipitates removed therefrom. The first precipitate from the filtrate with the original precipitate and other precipitates returned to the original mixture for reworking. The final filtrate will contain a relatively pure fraction of esters of fatty acids of relatively low melting points. The original precipitate together with the first precipitate from the filtrate may be warmed to provide a liquid mixture and then cooled to crystallize the esters of higher melting point in the mixture. The crystalline precipitate may be retained as the final product of highest melting point, while the filtrate may be returned to the original mixture for reworking.

As a specific example of the invention and referring particularl to the flow diagram shown in the drawing, a mixture of the ethyl esters of the fatty acids obtained from lard may be subjected to the crystallizing process. The mixture, for example, contained 1010 gms. of the esters and had an iodine number of 61.3. The liquid mixture of esters indicated at It! was cooled at C. for a period of 16 hours and filtered at 6 C. to remove the crystalline precipitate formed. The filtrate ll, constituting 799 gms. of material having an iodine number of 72, was cooled at C. for 16 hours and filtered at -5 C. The

precipitate [2 was combined with the precipitate [3 from the original filtration, while the filtrate Hi was further cooled. The filtrate I i, consisting of 714 gms. of material having an iodine number of '75, was cooled at 10 C. for 16 hours and filtered at 5" C. The filtrate [5 from this operation was found to consist of 600 gms. of material having an iodine number of 83 and consisted essentially of the ester of oleic acid. The precipitate [6 from the last filtration consisted of gms. of material having an iodine number of 32 and was returned to the original mixture for reworking.

The precipitate I2, consisting of 80 gms. of material having an iodine number of 37, was combined with the precipitate 13, consisting of 184. gms. of material having an iodine number of 15, and the combined mixture warmed to liquefy the same. The liquid mixture was then cooled at 6 C. for 16 hours and filtered at 6 C. The precipitate I! from this last operation consisted of 200 gms. of material having an iodine number of 8 and consisted essentially of stearic and palmitic acids. This precipitate was removed as the crystalline product, while the filtrate [8 obtained from the last step and consisting of 67 gms. of material having an iodine number of 62 was returned to the original mixture for reworking.

As another specific example of the invention, a mixture of fatty acids containing approximately 50% oleic acid and 50% linoleic acid, and

having an iodine number of 114, was cooled at 20 C. and filtered at 20 C. The filtrate having an iodine number of was cooled at 28 C. and filtered at 25 C. The filtrate from this operation was cooled at 22" C. and no precipitate was formed. This filtrate had an iodine number of 123. The precipitate from the first cooling step had an iodine number of 97, while the precipitate from the second step had an iodine number of 98. These precipitates were combined, warmed to form a liquid mixture, and cooled at 5 C. The mixture was filtered at -5 C., and the precipitate recovered was found to have an iodine number of 49. The filtrate from this last step had an iodine number of 114. This filtrate was returned to the original mixture for reworking.

With the process of the present invention, esters of fatty acids are separated according to their melting points. Since the melting points of the fatty acids correspond quite closely to the melting points of the esters and since the melting points of the fatty acids also correspond closely to the degree of unsaturation of the fatty acids, the process is effective to separate fatty acids into fractions according to the degree of unsaturation of the fatty acids.

With the present process, very readily separated crystals are easily formed and the various fractions may be efiiciently separated from each other without the use of a foreign solvent. The separation is much more efiicient than would be possible in the separation of the fatty acids themselves and is also much more efiicient than the separation of the methyl esters of the fatty acids. Accordingly, the crystallizing process is applied only to esters of the fatty acids in which the alcohol group of the ester contains at least two carbon atoms, and in this process a marked and striking improvement in the efiiciency of separation is obtained.

Although the invention has been described in connection with certain specific examples, it will be apparent thatmodifi'cationsand changes may be made without departing from the spirit and scope of the invention.

We claim:

1. A crystallizing process comprising providing a liquid mixture substantially free of foreign solvents and containing a mixture of esters of fatty acids, a monohydric alcohol group in each of said esters containing from two tofour carbon atoms, lowering the temperature of the liquid mixture to crystallize a relatively high melting portion of said esters, and separating the crystallized portion from the liquidmixture;

2. A crystallizing process comprising providing a liquid mixture of esters of fatty acids, a monohydric alcohol group in each of said esters containing from two to four carbon atoms, said mixture being substantially free of foreign solvents, lowering the temperature of the liquid mixture to crystallize a relatively high melting portion of said esters, separating the crystallized portion from the liquid mixture, further lowering the temperature of the remaining liquid mixture to crystallize a portion of lower melting point, and separating said portion of lower melting point from the liquid mixture.

3. A crystallizing process comprising lowering the temperature of a liquid mixture substantially free of foreign solvents and containing a mixture of esters of stearic, palmitic and oleic acids, a monohydric alchol group in each of said esters containing from two to four carbon atoms, to crystallize the esters of stearic and palmitic acid, and separating the crystallized esters from the liquid mixture.

4. A crystallizing process comprising lowering the temperature of a liquid mixture of the ethyl esters of fatty acids, said mixture being substan tially free of foreign solvents, to crystallize a relatively high melting portion of the esters, and separating the crystallized portion from the liquid mixture.

5. A crystallizing process comprising lowering the temperature of a liquid mixture of esters of oleic and linoleic acids, a monohydric alcohol group in each of the esters containing from two to four carbon atoms and the mixture being substantially free of foreign solvents, to crystallize the ester of oleic acid, and separating the crystallized oleic acid ester from the liquid mixture.

6. A crystallizing process comprising preparing a liquid mixture substantially free of foreign solvents and consisting essentially of esters of fatty acids, a monohydric alcohol group in each of said esters containing from two to four carbon atoms, lowering the temperature of the mixture to crystallize a relatively high melting portion of the esters, and separating the crystallized portion from the liquid mixture.

7. A process for the separation of fatty acids, comprising esterifying with a monohydric alcohol containing from two to four carbon atoms the fatty acids in a natural mixture of fatty acids, the mixture being substantially free of foreign solvents, lowering the temperature of the liquid mixture of the esters to crystallize a relatively high melting portion of the esters, separating the crystallized portion of the esters from the liquefied mixture, and separately hydrolyzing the esters of the crystalline precipitate and the remaining liquid mixture.

8. A crystallizing process comprising lowering the temperature of a liquid mixture substantially free of foreign solvents and containing the ethyl esters of a natural mixture of fatty acids to crysesters, and separating the crystallized portion of the esters from the liquid mixture.

9. A crystallizing process comprising providing aliquid mixture of esters of a natural mixture of fatty acids containing saturated fatty acids of relatively high melting point and unsaturated fatty acids of relatively low melting point, a monohydric alcohol group in each of said esters being the same and containing from two to four carbon atoms, the mixture being substantially free of foreign solvents, lowering the temperature of the liquid mixture until the bulk of the esters of the saturatedfatt acids are crystallized, and separating the crystallized esters from the liquid mixture.

10. A crystallizing process as set forth in claim 9 wherein the crystalline precipitate and the remaining liquid mixture are separately hydrolyzed to recover separately the fatty acids therein.

11. A crystallizing process comprising providing a liquid mixture substantially free of foreign solvents and containing a mixture of esters of fatty acids, a monohydric alcohol group in each of said esters containing from two to four carbon atoms, lowering the temperature of the liquid mixture to crystallize a relatively high melting portion of said esters, separating the crystallized portion from the liquid mixture, further lowering the temperature of the remaining liquid mixture to crystallize a portion of esters of lower melting point, separating the crystallized portion of lower melting point from the liquid mixture, subjecting the same to reworking, and recovering the remaining liquid mixture containing the esters of lowest melting point.

12. A crystallizing process comprising providing a liquid mixture substantially free of foreign solvents and containing a mixture of esters of fatty acids, a monohydric alcohol group in each of said esters containing from two to four carbon atoms, lowering the temperature of the liquid mixture to crystallize a relatively high melting portion of said esters, separating the crystallized portion from the liquid mixture, further lowering the temperature of the remaining liquid mixture to crystallize a portion of esters of lower melting point, separating the crystallized portion of lower melting point and adding the same to the separated crystallized portion of highest melting point, further lowering the temperature of the remaining liquid mixture to crystallize a portion of esters of lower melting point than said crystallized portions, separating said last-mentioned crystallized portion from the liquid mixture and subjecting said last-mentioned crystallized portion to reworking, and recovering the remaining liquid mixture containing the portion of esters of lowest melting point.

13. The crystallizing process as set forth in claim 12 wherein the temperature of the combined crystallized portions is raised to liquefy the mixture, the temperature of the liquefied mixture is lowered to crystallize the portion of esters therein of highest melting point, and said crystallized portion is separated from the liquid mixture,

14. A crystallizing process comprising a liquid mixture substantially free of foreign solvents and containing a mixture of esters of fatty acids, a monohydric alcohol group in each of said esters containing from two to four carbon atoms, lowering the temperature of the liquid mixture to crystallize a relatively high melting portion of said esters, separating the crystallized portion from the liquid mixture, raising the temperature 7 8 of the separated crystallized portion of esters to Y UNITED STATES PATENTS liquefy the same, lowering the temperature of the Number Name Date liquefied portion to crystallize the portion of es 1 659 790 Stands Feb 21 1928 ters therein of highest melting point, and sepa- 2113960 Grote 1938 rating said last-mentioned crystallized portion 5 2308848 Young 1943 from the liquid mixture associated therewith.

W LL POOL OTHER REFERENCES ROGER SEDGWICK- Brown, J. B., "Low-Temperature Crystalliza- 10 tion of the Fatty Acids and Glycerides, Chemical Reviews, vol. 29, pages 336-337 (1941). REFERENCES CITED Jamieson, Vegetable Fats and Oils, 2nd edi- The following references are of record in the tion,p ge 148 (1943), Rei hold C0. file of this patent: Malkin, Journal of the Chemical Society (London), pages 2796-2805 (1931). 

1. A CRYSTALLIZING PROCESS COMPRISING PROVIDING A LIQUID MIXTURE SUBSTANTIALLY FREE OF FOREIGN SOLVENTS AND CONTAINING A MIXTURE OF ESTERS OF FATTY ACIDS, A MONOHYDRIC ALCOHOL GROUP IN EACH OF SAID ESTERS CONTAINING FROM TWO TO FOUR CARBON ATOMS, LOWERING THE TEMPERATURE OF THE LIQUID MIXTURE TO CRYSTALLIZE A RELATIVELY HIGH MELTING PORTION OF SAID ESTERS, AND SEPARATING THE CRYSTALLIZED PORTION FROM THE LIQUID MIXTURE. 